The slides present a very brief introduction to Electric Current.

1. Electric Current
by
SBR
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2. Electric Current
• Electric current is the rate of flow of charge through a conductor of cross-sectional area 𝑨.
• In electric circuits this charge is often carried by electrons moving through a wire.
• It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an
ionized gas (plasma).
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3. Unit of Current
• The conventional symbol for current is 𝑰
• If ∆𝑸 is the amount of charge passing through an area in a time interval ∆𝒕, then the
average current 𝑰 𝒂𝒗𝒆 is defined as:
𝑰 𝒂𝒗𝒆 =
∆𝑸
∆𝒕
=
𝒅𝑸
𝒅𝒕
• The unit of current is coulomb per second.
• also called the ampere (𝑨).
𝟏𝑨 =
𝟏𝑪
𝟏𝒔
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4. Unit of Current
• Ampere is a large unit.
• Therefore, the current is usually expressed in:
𝑚𝑖𝑙𝑙𝑖𝑎𝑚𝑝𝑠 (1 𝑚𝐴 = 1 × 10−3
𝐴)
𝑚𝑖𝑐𝑟𝑜𝑎𝑚𝑝𝑠 (1 µ𝐴 = 1 × 10−6
𝐴)
𝑛𝑎𝑛𝑜𝑎𝑚𝑝𝑠 (1 𝑛𝐴 = 1 × 10−9
𝐴)
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5. Conventions
• In a conductive material, the moving charged particles that constitute the electric current are
called charge carriers.
• In metals, which make up the wires and other conductors in most electrical circuits, the
positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively
charged electrons are the charge carriers, free to move about in the metal.
• In other materials, notably the semiconductors, the charge carriers can be positive or
negative, depending on the dopant used.
• Positive and negative charge carriers may even be present at the same time, as happens in
an electrolyte in an electrochemical cell.
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6. Conventions
• A flow of positive charges gives the same electric current, and has the same effect in a
circuit, as an equal flow of negative charges in the opposite direction.
• Since current can be the flow of either positive or negative charges, or both, a convention is
needed for the direction of current that is independent of the type of charge carriers.
• The direction of conventional current is arbitrarily defined as the same direction as positive
charges flow.
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7. Conventions
• The electrons, the charge carriers in an electrical circuit, flow in the opposite direction of the
conventional electric current.
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Flow of Positive Charge
Flow of Electrons

8. What is enough current?
Note:
around 100 mA to 1 A of current is sufficient to
induce cardiac/respiratory arrest.
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Device Current (A)
(A)
100-W lightbulb 1
Microwave 8 – 13
Laptop 2 – 3
Electric Fan 1
Television 1 – 3
Toaster 7 – 10
Fluorescent Light 1 – 2
radio/stereo 1 – 4
typical LED 20 X 10-3
Smart Phone 200 X 10-3
automobile starter 200
Lightning 1000